I. Field of the Invention
The present invention relates to a container for carrying disk-shaped articles, such as data storage disks, substrate wafers, and the like. More particularly, the present invention relates to an improved disk cassette for data storage disks having a plurality of adjacently disposed rib members, wherein each rib member has an improved cross-sectional profile such that engagement grooves defined therebetween have a dual angle configuration which maintain each data storage disk in radial contact at four different areas along the chamfered periphery thereof to minimize particulation from forming within the disk cassette.
II. Description of the Prior Art
For years, manufacturers have produced special containers for transporting, storing, and processing data storage disks, substrate wafers, and the like. The common denominator with such articles is that they are particularly sensitive to contamination and therefore require extraordinary care when handling to avoid such exposure. Although the containers may be provided with cover members for safeguarding the disks from external impurities, a significant threat of contamination arises within the container itself in the form of airborne particulate which may settle on the disks and cause imperfections. Particulate constitutes subminiature fragments of the material used to manufacture the disk cassette and stems from the abrasion which occurs between the disk cassette and the disks when the disks experience disk tilt within the disk cassette. Main sources of disk tilt include movement of the disk cassette, such as during transportation and handling, as well as thermal expansion of the disks and/or disk cassette, such as during processing.
With regard to data storage disks, particulate has the effect of tainting the data storage medium which results in a reduced ability to store and/or retrieve data. Although several disk cassettes have been specifically designed to accommodate data storage disks during transportation, storage, and processing, these prior art attempts have significant drawbacks which precipitate the need for the present invention. For example, U.S. Pat. No. 4,779,732 to Boehm et al. discloses a disk package for data storage disks including a two-part disk cassette, a top cover, and a bottom cover, wherein each half of the disk cassette has a plurality of rib members. This arrangement is disadvantageous for several reasons. First, the cross-sectional profile of the rib members provides a uni-angular engagement groove defined between the adjacent rib members which permits a considerable degree of disk tilt. Second, the disks must be supported at a plurality of different contact points in both the upper and lower hemisphere in order to compensate for the disk tilt which results from the uni-angular engagement grooves. This has the effect of increasing the contact area between each disk and the disk cassette which, it will be appreciated, increases the likelihood for abrasion and therefore particulation. Requiring rib members in both the upper and lower hemisphere also increases the cost of manufacture, both in terms of the increased amount of material required as well as the increased cycle time for curing which, in turn, limits production.
U.S. Pat. No. 4,557,382, issued to Johnson and assigned to the applicant's assignee, discloses a disk cassette for memory disks having a plurality of parallel rib members defining engagement grooves therebetween. Although generally effective, this disk cassette also has drawbacks from the standpoint of particulate generation and expense of manufacture. With regard to particulation, the cross-sectional profile of the rib members forms a single angle within each engagement groove which, as noted above, causes the data storage disks to experience a fair degree of disk tilt during transportation and handling. In this same regard, a relatively large contact area exists within each engagement groove which also increases the opportunity for abrasion and thus particulation. With regard to manufacturing costs, the disk cassette requires a relatively large amount of material which translates into increased costs for materials, as well as increased cycle time for curing which, as noted above, limits the number of disk cassettes which can be produced within a given period.
A need therefore exists for an improved disk cassette which solves the aforementioned problems with the disk cassettes disclosed in the prior art. In particular, an improved disk cassette is needed which restricts the mobility of the disks within the disk cassette so as to reduce abrasion and, hence, particulation. A need also exists for an improved disk cassette which boasts minimal contact area between each disk and the disk cassette so as to reduce the propensity for particulation. A need also exists for an improved disk cassette which is streamlined in terms of the amount of material required for manufacture, thereby decreasing the cost of materials, the cycle time for curing, and overall cost of manufacture.